A predator achieves apex predator status when others in its habitat no longer consider it prey, or only attack in the most extreme circumstances. For instance, killer whales sometimes attack great white sharks, but both remain apex predators because such an event is extremely rare. But the apex predator classification is not absolute. Given the chance, some apex predators, such as the tiger, will prey on humans, while tigers, in turn, may certainly be hunted by humans.

Apex predators may also find themselves demoted to lesser status in unfamiliar surroundings. Being highly attuned to their environment, apex predators may easily become prey to species outside of their normal ecosystem. A common example is the domestic housecat, an apex predator domestically, but a prey species to coyotes in the wild.

Apex predators are often “keystone species,” with a disproportionately large effect on their environment relative to their abundance. Introduction or removal of such an apex predator into an ecosystem can have drastic effects on that system’s equilibrium.